Medical biochemistry

Question 1

Select three of the enzymes involved in the process of DNA replication, and for each one
explain their role/function in the process.

Answer 1

Helicase (unwinds and opens up helix)
Stabilizing proteins (stabilize the single stranded DNA section)
Primase (makes RNA primer)
DNA polymerase (elongation)
Another DNA polymerase
(removes primer, replaces it with DNA)
Ligase (links the 3’-hydroxyl and 5’-phosphate groups of Okazaki fragments)

Question 2

41. Outline the “central dogma of information transfer” and explain the function/role of each
    element in the dogma.

Answer 2

DNA → RNA → protein (0.5)
DNA carries the genetic code/information and is stable and protected (1), RNA is unstable
and transfers the information from the DNA (1), and protein is the functional component
putting the information into use (0.5).

Question 3

42. Remodelling of damaged tissue to repair a wound requires the production of proteins and
    the laying-down of an extracellular matrix. Identify the factors/elements involved in
    initiating and executing gene transcription, and explain the role of these factors/elements in
    the process of transcription.

Answer 3

Each gene contains a promoter sequence (0.5) that is recognized by transcription factors
(0.5) that together with RNA polymerase (0.5) forms a complex necessary for transcription
to start.
Promoter as the controlling point of transcription, signals the starting point of transcription.
(0.5)
Transcription factors: Proteins that recognize and bind to promoters. Different promoters
require different TFs. Availability. (1)
RNA polymerase: Opens up DNA helix. Transcribes the template strand (works 5’→3’).
Closes the helix as it passes. (1)

Question 4

15. Explain the term “semi-conservative” with respect to replication of DNA. (1 mark)

Answer 4

When the double-helix replicates, each of the two daughter molecules will have one old
strand (derived from the parent molecules) and one newly made strand (from free
nucleotides in solution).

Question 5

16. Explain what is meant coding and non-coding strands of DNA. (2 marks)

Answer 5

The DNA non-coding strand serves as the template for mRNA synthesis. Therefore, the
coding strand is the strand of DNA that has the same sequence as the mRNA.

Question 6

State what telomeres are and outline their function

Answer 6

Telomeres are repetitive nucleotide sequences at each end of a chromosome, which
protects the end of the chromosome from deterioration (acts as “buffer” for shortening
of chromosomes with each round of replication).

Question 7

List the three processing steps for mRNA in eukaryotes.

Answer 7

Capping at the 5’ end; addition of a poly A tail; splicing to remove introns